<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        #win {
            
            position: fixed;
            top: 50%;
            left: 50%;
            z-index: 99;
            width: 200px;
            line-height: 50px;
            margin: -30px 0 0 -100px;
            font-size: 15px;
            color: #fff;
            background-color: #242323;
            text-align: center;
            opacity: 0;
            transition: opacity 500ms 10s ease;
            -webkit-border-radius: 5px;
            border-radius: 5px;
        }
        
        #win.win-active {
            
            opacity: .72;
        }
    </style>
</head>
<body>
<div id="win" class="win-active"></div>
<script>

    function show() {

        var win = document.getElementById('win');

        win.innerText = "Hello!";
    }
    
    if (window.localStorage) {

        var local = window.localStorage;

        var time = local.getItem("time");

        if (time == null) {

            show();

            local.setItem("time","1");
        }
    }
</script>
</body>
</html>